Existing highway guardrail end treatment systems include: the breakaway cable terminal (BCT), the eccentric loader terminal (ELT), the modified eccentric loader terminal (MELT), the vehicle attenuating terminal (VAT), the extruder terminal (ET 2000 and ET plus), the slotted rail terminal (SRT), the sequential kinking terminal (SKT) and the flared energy absorbing terminal (FLEAT).
Terminal ends (that is, the end facing oncoming traffic) generally consist of one or more, often three, W shaped (in cross-section) guardrails supported by a series of both controlled release terminal (CRT) or frangible posts and standard highway guardrail posts. Generally a cable assembly arrangement is utilised that anchors the end of the rail to the ground, transferring tensile load developed in a side-on impact by an errant vehicle to the ground anchor. Generally the terminal ends have an impact head arrangement that will be the first part impacted by an errant vehicle during an end-on impact which is designed to spread or absorb some of the impact energy.
Some terminal ends such as the abovementioned ET, SKT and FLEAT, absorb the energy of the impacting vehicle during an end on impact by having an impact head that slides down the W shaped guardrails, extruding it and breaking away the support posts as it travels down the rails. All of the other abovementioned terminal ends work on the principal of various weakening devices in the posts and rails to allow an errant vehicle to penetrate the terminal end in a controlled manner and prevent the rails from spearing the vehicle or the vehicle from vaulting or jumping over a relatively stiff terminal end.
All of the abovementioned guardrail terminal ends are considered to be gating, that is, if impacted between the impact head and the “length of need” (where the “length of need” is considered to be the distance from the terminal end to where the guardrail will redirect a vehicle during an angled impact) during an angled impact, the terminal end will gate and allow the errant vehicle to pass to the back side of the terminal end. However this gating effect may have undesirable or unsafe results, and preferably an improved or safer or varied energy absorbing system is utilised to control errant vehicle barrier/guardrail impacts.
It is therefore an object of the present invention to provide a guardrail and/or guardrail impact head which will go at least some way towards addressing the foregoing problems or which will at least provide the industry with a useful choice.
All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.
It is acknowledged that the term ‘comprise’ may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, the term ‘comprise’ shall have an inclusive meaning—i.e. that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or elements. This rationale will also be used when the term ‘comprised’ or ‘comprising’ is used in relation to one or more steps in a method or process.
Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.